Microelectronic packages for power transistors have included an alumina ceramic substrate on whose top surface is disposed a metal heat sink such as copper onto which the die is attached, and two metallized pads to which leads are attached and the die is wire bonded. A metal heat sink, again such as copper, is disposed on the bottom surface of the ceramic substrate. The finished assembly is utilized in electronic apparatus containing circuit boards. The circuit board generally has cavities for accepting the power transistor package, and the bottom heat sink is placed in thermal contact with a heat sink located at the bottom of the cavity of the circuit board.
Although the metal heat sinks are useful in conducting heat away from the power transistor device while in operation, the mismatch between the thermal expansion coefficient of the material of the power device and the top metal heat sink, and between the ceramic and both metal heat sinks can cause failure of the bonds between these elements during thermal cycling experienced in operation. The same problems encountered with metal heat sinks are experienced in the prior art where beryllia is utilized as a substrate material.
Further, the packages of the prior art must be oriented in a particular position for assembly, due to the asymmetric distribution of package elements. This lessens the capability of the package to be easily assembled by automated equipment, and requires complex apparatus for positioning the substrate for processing.
It is therefore an object of the present invention to provide a microelectronics package without a significant thermal expansion coefficient mismatch between the package elements.
It is a further object of the present invention to provide a microelectronics package which is easily assembled by automated processing.
These and other objects and advantages of the invention set forth herein are accomplished by the present invention as described in the Specification and Claims which follow.